2 stroke thread (with occasional F1 relevance!)

[manolis]

Hello Pinger.

You write:
"Superficially at first glance yes. But that version is countering the back shift resistance by further forcing load onto the front driven pulley. The compression forces within the belt as it passes over that pulley will be increased - possibly to its detriment."



The typical modification of a scooter (there are millions of them on the roads) is the substitution of the variator (governor) by an “aftermarket” having different characteristics than the original one.

In most cases the rider is looking for something improving the performance of his scooter. Then he regrets, because there are side effects, but it is late.


The original variator of a scooter is, typically, a compromise for:
relatively acceptable fuel efficiency (mileage),
relatively acceptable acceleration,
relatively acceptable final speed,
relatively acceptable reliability,
relatively acceptable climbing ability,
relatively acceptable NVH (noise vibrations harshness) properties etc.


For better mileage, quieter riding (long trips on the highway), improved reliability and the similar, the CVT should keep the engine at substantially lower revs. But then the acceleration, the climbing capacity with heavy load, the overtake ability and the similar are hurting.

If, on the other hand, the focus is on the performance, on the safety (accelerations, faster overtake etc) the CVT has to keep the engine at higher revs, which means that the mileage drops, the noise – in a long ride – gets exhaustive, the reliability worsens etc.


During a long ride on the highway, a rider who replaced his variator by a sporty one, or the "weights" of his original variator by lighter ones, is missing his previous CVT setting.

During an acceleration / overtake, the rider who didn’t replaced his variator by a sporty one, regrets for his choice.


In most cases the rider of a scooter (just like the rider of a car; think: when it was the last time you operated your engine at its peak power revs?) needs longer and way longer transmission ratios.
Only from time to time (say during a fast ride, or a dangerous overtake) the rider of the scooter does need shorter gear ratios to get the most from his engine.


Suppose you have a scooter and you want to get the best from it, without compromises.

You start by replacing the variator with one providing longer transmission ratios (you can alternatively replace the weights of the variator by heavier ones).

The longer-geared-CVT keeps the engine at lower revs, the fuel efficiency is higher, the noise drops, the scooter gets more reliable.

However, when you want to go faster, when you go overloaded on an uphill with strong opposite wind, when you need to overtake a long truck, things get from tough to dangerous, making the long-geared-CVT a bad choice.


Now let’s see how the PatBox can improve the above long-geared-CVT scooter.

By adding an auxiliary belt and a lever, the CVT turns to PatBox (stereoscopic representation, more on how to look at it at http://www.pattakon.com/pattakonStereoscopy.htm ) :



The auxiliary belt is “standby”.
It rides around the external periphery of the V-belt and follows its rotation without resistance (or, more correctly, with very small resistance / friction, because the auxiliary belt is not transmitting any torque; all it does is to push the V-belt deeped in the front pulley, and this is necessary only when the long-geared-CVT proves too long for the existing conditions).


Any moment the rider needs a faster acceleration than what the long-geared-CVT can offer, he just presses the PatBox lever and the auxiliary belt pushes the V-belt deeper in the front pulley.

Alternatively he can “preload” the spring that pulls the lever that pulls the auxiliary belt (this means “automatic operation” with shorter gear ratios, which is one of the characteristics of the PatBox: it can run manual or automatic).



The overall gain in running cost (fuel, V-belt wear etc) and quietness is more than significant, without sacrificing the safety or the performance.


Do I miss something?

What are the problems you see in a modification like the previous?

If the PatBox achieves the reduction by, say, 25% of the running cost of a scooter, on the expense of a heavier pressing of the V-belt in the front pulley from time to time, isn't the pain worth the gain?




Here is a couple of comments on another forum (Mopeds Army) from the guy (a third party) who first made, and tested on his 50cc moped, a PatBox CVT :

“This design is not difficult to make at all, and shifts like butter.”

and

“As for eating power, it might, but my bike is faster now.
I can say that my hobbit is faster now than it was before.
Substantially.
Not having to accommodate for rpm drop at high speeds because you can manually adjust opens so many new tuning avenues.”


Thanks
Manolis Pattakos

[Tommy Cookers]

[quote=Pinger]
What peeves you about lock-up convertors? Admittedly they introduce an element that can (and sometimes do) fail, but given the efficiency gain...[/quote]

not knowing whether it's locked or not
in earlier cars (rentals) one could evolve to stay in the lock, and usefully some clonked when unlocking
my current car is so responsive and seamless it doesn't want to stay in lock and one doesn't know whether it's in lock or not

arrangements may have been more positive in the Chaparral 2F

[gruntguru]

According the torque curve of the Yamaha RD350LC (page 137, top),
if you do the same holding the engine at 6,500rpm (where the engine makes 49mN, i.e. some 10% more than at 6,000rpm),
you will burn a little more friction material in the clutch,
you will heat the clutch a little more,
however until 45Km/h (fully engaged clutch in both cases) you have some 10% higher acceleration, which means that you gain some 0.1 seconds of time and some 1.2m of distance.

Assuming of course the extra torque can be fed to the ground without losing traction or popping a wheelie.

When the peak torque is insufficient to break traction, the clutch can be further abused by revving the engine even higher and maintaining the clutch at the traction limit while the revs decrease. The stored energy in the flywheel is released to increase the torque at the rear wheel(s) and destroy the clutch. Once the revs drop to the torque peak the clutch setting should be reduced to hold the revs there until the rear wheel catches up.

[gruntguru]

& following its best run in the test under consideration, had conniptions requiring a 'tear down' - tout suite..

I have just read the article and it appears the dyno test on the 900 was performed after the tear down, so it seems the dyno power figure may have been lower than the power it had for the 1/4 mile run.

Clearly the 903 had produced more horsepower on the drag strip than it had on the dynamometer. Why? Nobody knew—but bear in mind that the Z1 had been dismantled right before it went on the pump, and had been reassembled without the benefit of new rings or new valve guide seals, because no fresh parts existed for the brand-new four-cylinder. The Z1 had been sharp as a tack at the strip; mechanic Jeff Shelter felt that its fine-tune had evaporated during the reassembly.

[J.A.W.]

Yes - gg, & that seemingly odd circumstance - raises a couple of technical points..

Was the marked improvement in 1/4 mile performance - by the very same machine - from the previous test..
..gained due to merciless hammering, which then showed as damage/impairment on the dyno?

Or was the demonstrable 1/4 mile improvement - due to altered cam settings*, giving more rpm..

&, in the 'tear down' - an opportunity was taken to return the cam-timing back to standard specs..
..even though it would indeed - make less power on the dyno - 'truth machine'..
..but knowing that the post-test technical inspection, absolutely had to be passed as a 'kosher' unit..

The 'machinations' are more than merely technical in these instances, I can assure you..
..even if the mag had to be 'circumspect', esp' given the big ad splurge Kawasaki had paid for - in it..

* A well-known 'dodge' in 'showroom stock/production racing' circles at the time, & facilitated by DOHC..

[J.A.W.]

According the torque curve of the Yamaha RD350LC (page 137, top),
if you do the same holding the engine at 6,500rpm (where the engine makes 49mN, i.e. some 10% more than at 6,000rpm),
you will burn a little more friction material in the clutch,
you will heat the clutch a little more,
however until 45Km/h (fully engaged clutch in both cases) you have some 10% higher acceleration, which means that you gain some 0.1 seconds of time and some 1.2m of distance.

Assuming of course the extra torque can be fed to the ground without losing traction or popping a wheelie.

When the peak torque is insufficient to break traction, the clutch can be further abused by revving the engine even higher and maintaining the clutch at the traction limit while the revs decrease. The stored energy in the flywheel is released to increase the torque at the rear wheel(s) and destroy the clutch. Once
the revs drop to the torque peak the clutch setting should be reduced to hold the revs there until the rear wheel catches up.

Of topical interest is this Kevin Cameron piece..
In the 4th paragraph he gives the 'official' Kawasaki advice for young Americans to launch their high-strung 2Ts..
& without having to concern themselves with issues involving such finesse as proper clutch/throttle
modulation..

[manolis]

Hello J.A.W.


According Kevin Cameron, the technique for launching an H1, as demonstrated by official Kawasaki service personnel, was:

“. . . Bring the revs up and drop the clutch, setting the tire spinning and smoking, then sit down, holding the revs at peak torque, and rocket away”


I.e. as in the graph “Hard Use of Clutch”, top of page 137 (post #2040), wherein from 0Km/h to 50Km/h the clutch is slipping with the engine revving at its peak torque rpm and with the throttle fully opened.

The result is the constant force of 263Kp (580lb) that accelerates the motorcycle / rider until the full engagement of the clutch.

Thanks
Manolis Pattakos

[manolis]

Hello Gruntguru.

You write:
“Assuming of course the extra torque can be fed to the ground without losing traction or popping a wheelie.
When the peak torque is insufficient to break traction, the clutch can be further abused by revving the engine even higher and maintaining the clutch at the traction limit while the revs decrease. The stored energy in the flywheel is released to increase the torque at the rear wheel(s) and destroy the clutch. Once the revs drop to the torque peak the clutch setting should be reduced to hold the revs there until the rear wheel catches up.”


Exactly.

And this happens not only at launching, but also during the gear shifts.

The kinetic energy stored in the moving parts of the power train is used to accelerate the vehicle during the coupling of the clutch for the next gear ratio.


Here is the yourube video of the pattakon VVA-roller Honda Civic accelerating on the road:

https://www.youtube.com/watch?v=-zzW8YkReLU



(more at http://www.pattakon.com/pattakonRoller.htm )


Shifting from 1st to 2nd the revs of the engine / flywheel have to drop from 9,000rpm to 7,600rpm.

Someone or something has to absorb this energy.

During the coupling of the clutch, the kinetic energy of the moving parts (flywheel, crankshaft etc) is absorbed by the vehicle and its speed increases before opening the throttle for the second gear.

It is the 7th second in the video (replay the video looking at the tachometer and speedometer).

Thanks
Manolis Pattakos

[J.A.W.]

As always I agree J.A.W. The facts from this "real world" test are:

The 2T with tricked gear ratios for the 1/4 mile and a massive weight advantage set effectively the same ET as a stock 4T. I've shown conclusively why - it's takes a little grey matter to understand though so I completely understand why it's gone over your head.

Moreover there are the driveability problems of the 2T which are detailed in the linked page as well as this little gem:

When the dyno testing had been completed, only one motorcycle-—the 903—left us puzzled. Both it and the Mach IV had produced nearly identical quarter-mile figures –low twelves at 110 mph—and both had produced 64 horsepower on the dynamometer. But the 903 didn’t have the Mach IV’s gearing advantage, and it had to deal with a weight penalty of 73 pounds.

...


Actually T.W., Cycle Mag put the test outcome fact summary,( verbatim) this way..

..after succinctly noting that: "Yamaha's dyno' revealed hogwash-free engine performance data."
..they concluded..

" ...the Kawasaki Mach IV 750, the winner outright & ruler, without question."
&,
"It was also the most fun to ride, a wild & skittish bucking bronco, with all the talent in the entire world,
& not a single ounce of condescension."

[J.A.W.]

Hello J.A.W.


According Kevin Cameron, the technique for launching an H1, as demonstrated by official Kawasaki service personnel, was:

“. . . Bring the revs up and drop the clutch, setting the tire spinning and smoking, then sit down, holding the revs at peak torque, and rocket away”


I.e. as in the graph “Hard Use of Clutch”, top of page 137 (post #2040), wherein from 0Km/h to 50Km/h the clutch is slipping with the engine revving at its peak torque rpm and with the throttle fully opened.

The result is the constant force of 263Kp (580lb) that accelerates the motorcycle / rider until the full engagement of the clutch.

Thanks
Manolis Pattakos

Ah, not quite Manolis..

In the instance noted by K.C., the term "drop" indicates a fully engaged clutch/transmission..
& thus, it is the spinning rubber - which is doing the job of, somewhat crudely, - 'paying-out' the power..

[manolis]

Hello J.A.W.

You write:
"In the instance noted by K.C., the term "drop" indicates a fully engaged clutch/transmission..
& thus, it is the spinning rubber - which is doing the job of, somewhat crudely, - 'paying-out' the power.."


My mistake. Thanks J.A.W.


So, the slipping is not happening in the clutch, it happens between the spinning rubber of the rear tire and the road.

In both cases a "clutch" is required between the engine and the road.

I suppose that with fully loaded motorcycle (Kawasaki H1), the splipping is shifted to the normal clutch.


Either with the normal clutch, or with the rear tyre acting as the clutch, the maximum possible accelerating force is as in the graph of post #2040.


However,

In cases like that of the Kawasaki H1, wherein the maximum friction force Fmax between the rear tire and the road is lower than the calculated accelerating engine force, the basic curve should be limited to no more than Fmax.


This means than one more parameter is required for the RoadLoad program for cases like the H1: it is the maximum force the rear tyre can apply to the road.


Thanks
Manolis Pattakos

[J.A.W.]

Hi Manolis..

In the instance cited, with the tyres as factory fitted by Kawasaki back then..

I can confidently state from experience, that no, the clutch won't fail..
..indeed a 2nd gear 'burn-out'.. being a 'grandstanding/showboating' spectacle that deliberately..
..(abused the machine)..by being held stationary on the front brake, kept spinning, & brake, slowly released..
..made for a typical young 'motorhead' sensory display of 'skill/foolhardiness'..

With the powerful Kawasaki triples however, part of the skill involved management of the 'wheelie'..
..that might well result from the 'rolling burn-out', as the heat softened/sticky tyre gripped & 'hooked up'..

Contemporary heavier, flat-torque 4T motorcycles were much less "bucking bronco/skittish" in these evolutions..
..but also accordingly less rewarding, if you 'really dig' the reaction-time training/adrenaline-shot 'hit'.. man..

[Pinger]

because the auxiliary belt is not transmitting any torque; all it does is to push the V-belt deeped in the front pulley,
What are the problems you see in a modification like the previous?

As I said previously ie, ''countering the back shift resistance by further forcing load onto the front driven pulley. The compression forces within the belt as it passes over that pulley will be increased - possibly to its detriment."

The 'pinch force' (sledders terminology - they are the masters of CVT clutch tuning) from the front pulley will be increased when the belt is forced down the sheaves and as the rpm rises, more so.
Before the days of torque sensitive secondary clutches, the only option to get the required pinch force for adequate belt grip under high torque transmission was high spring preload (on the secondary) to create pinch. This shredded belts.
Possibly on scooters this problem wont arise but on a high powered sled I suspect shortening of belt life wouldn't be welcomed. Try it and see I guess...

edit PS.
I guess the difference is that the high spring preload was prevalent all the time - even when torque transmission was low. Hence the belt shredding. In your design, the high pinch forces will only be present when effecting a downshift.
It's not how I'd have set about tackling this but it seems you have added 'kickdown' functionality to the simple CVT. A first I think.

[manolis]

Hello J.A.W.

You write:
“I can confidently state from experience, that no, the clutch won't fail..
..indeed a 2nd gear 'burn-out'.. being a 'grandstanding/showboating' spectacle that deliberately..
..(abused the machine)..by being held stationary on the front brake, kept spinning, & brake, slowly released..
..made for a typical young 'motorhead' sensory display of 'skill/foolhardiness'.”


With the rear tire slipping on the road, during launching, not only with the 1st gear but also with the 2nd gear, I wonder what is the meaning for using the 1st gear?

Reasonably the best time for 0-400m (a quarter of a mile) should be achievable starting with 2nd gear (and so avoiding the 1st to 2nd gear shift).

Do I miss something?

Thanks
Manolis Pattakos

[J.A.W.]

For those who may be interested in a stylish period presentation from nearly 1/2 a century ago ( ok, 45 years)..
..this glossy Kawasaki factory feature shows the brief moment in time..
..when 2T tech ruled the performance bike scene.. & not just in G.P./MX racing..
.. but even as presented for road use in the showroom..
..ah, the golden.. unashamed.. pre oil-shock.. `70s..

https://www.youtube.com/watch?v=pdhpuBby1Oo

(&, for those who like to skim, scroll forward to 3:30 in - to see the big 2T 'superbike' H2- in mass production).